Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

108
FXUS63 KLOT 230004
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
704 PM CDT Wed Apr 22 2026

.KEY MESSAGES...

- Isolated to perhaps widely scattered showers/storms this
  afternoon and early evening mainly across parts of northwest
  Indiana.

- Fog possible near the lake tonight.

- Warm, breezy, and dry areawide Thursday, with minor lakeshore
  cooling perhaps hanging on near the Lake Co. IL shore.

- More widespread showers and scattered thunderstorms with
  another cold front very late Thursday night into Friday.

- Seasonable and dry conditions over the weekend, then shower
  and thunderstorm chances return Sunday night and Monday.

&&

.DISCUSSION...
Issued at 244 PM CDT Wed Apr 22 2026

Through Thursday:

Scattered thunderstorms took off earlier over southeast Lake
Michigan and then spread into northern Indiana and southern
lower Michigan. As of this writing, the lake assisted cold
front extends from McHenry County IL to the Kankakee River
Valley of Indiana. Given the proximity of this boundary and
upper 50s to around 60F dew points east of I-57 in eastern
Illinois and interior northwest Indiana, 500-1000 J/kg of MLCAPE
may be realized by mid to late afternoon. We`ll need to keep an
eye on isolated to widely scattered shower and non-severe
thunderstorm development. If thunderstorms develop, slow storm
motions would portend locally heavy rainfall. Finally, as noted
in the previous discussion, conditional to convection initiation,
favorable parameters near the boundary for weak lower level
spin could conceivably yield a funnel cloud or two.

Once any showers and storms fade diurnally this evening, the
main focus through tonight is the potential for fog to bleed
inland from the lake and/or fog development in northeast
Illinois and far northwest Indiana. There`s a window from the
evening into the early overnight when flow just off the deck
will be quite light, especially closer to the lake. With the
existing bank of fog out over the lake this afternoon, as the
marine influenced boundary layer quickly cools this evening,
onshore flow could help drive fog and very low stratus inland.
Any patchy dense fog should tend to favor the late evening until
a few hours after midnight. Thereafter, increasing southwesterly
flow off the deck should result in the fog and stratus
retreating northward. Overnight lows will be mild inland, in
the mid to upper 50s, and in the mid to upper 40s near the lake,
prior to rising prior to daybreak Thursday.

The surface pattern over the eastern CONUS will hold off
appreciable moisture return until late in the day Thursday.
Strong surface low lifting into the Canadian Prairies and its
approaching cold frontal trough will tighten up the pressure
gradient. Expect a good deal of sunshine until late day high
level cloud cover arrival. These ingredients point to a breezy
(south-southwesterly gusts up to 25-35 mph) and summer-like
warm day, with highs near to likely above 80F for much of the
area. The possible exception may be the immediate Lake County IL
shoreline if winds back a bit due to lake influence. Dew points
are expected to mix out into the low-mid 50s during peak
heating, which may contribute to localized mid 80s highs,
especially in parts of central Illinois.

Thursday Night through Friday:

Showers and thunderstorms will develop well to our west through
Thursday afternoon on the aforementioned cold front and will
then track eastward into our area late Thursday night into early
Friday morning. Given the unfavorable diurnal timing and the
progged instability/shear parameter space remaining unimpressive
locally, the severe threat appears low. Can`t completely rule
out strong/gusty winds from a bit earlier arriving outflow
associated with decaying convection, particularly west of the
Fox Valley. The current setup does not appear favorable for
widespread convective maintenance and an appreciable heavy
rainfall threat. However, given the heightened sensitivity to
additional rainfall in areas hard hit by river flooding, we`ll
certainly keep a close on trends in this regard.

The southeastward progression of the cold front on Friday is a
bit of a question mark, with the faster solutions likely
limiting renewed convective development late Friday morning into
early Friday afternoon to our southeast CWA. Meanwhile, slower
solutions would bring the threat for renewed scattered storms
farther west. Barring stronger than expected destabilization,
the threat for strong to severe storms should remain south of
out area. The late day into the evening hours should feature a
quick improving trend (especially I-55 and NW) as much drier
air punches in behind the front crossing our IL counties.

Castro/Carlaw


Friday night through Wednesday:

Surface cold front should be exiting the forecast area Friday
evening, with any lingering showers southeast of I-55 ending as
the primary mid-level short wave wraps northeastward around the
closed low over southern Saskatchewan. While height rises are
fairly minimal behind this wave, models and their ensembles do
depict strong drying through the column in both soundings and
precipitable water forecasts. Thus despite the persistence of
fast west-southwesterly flow aloft, organized precipitation
chances appear minimal from Friday night through Sunday, while
weak surface high pressure ridge drifts east across the region.

There is decent ensemble agreement in depicting another strong
mid-level short wave out of the southwestern CONUS and across
the Plains Sunday, which induces renewed low-level southerly
flow and associated warm/moist advection into the region Sunday
night into Monday, ahead of a deepening surface low which lifts
into the upper Midwest/western Great Lakes region by Monday
afternoon/evening. Based on the track of the surface low, a
strong upper level jet and tapping of low-level moisture off of
the western Gulf (12Z ECMWF forecast precipitable water values
in excess of 1.50-1.60"), this will be a period to monitor for
potential severe weather and locally heavy rainfall threat in or
near the forecast area. Current guidance is then in decent
agreement in dry weather returning for Tuesday and Wednesday of
next week, as surface high pressure builds in behind the
departing deep low and surface cold front which looks to move
east of the area Monday night.

Temperatures appear seasonably mild Saturday into Monday, with
upper 60s to mid-70s for highs (except cooler 50s along the lake
with onshore flow Saturday-Sunday). Cooler 60s (still about
average for late April) are then expected behind the cold front
Tuesday into Wednesday.

Ratzer

&&

.AVIATION /00Z TAFS THROUGH 06Z FRIDAY/...
Issued at 704 PM CDT Wed Apr 22 2026

- Light fog is possible tonight, especially after midnight for
  the immediate Chicago area terminals.
- Moderately gusty southerly winds are expected late morning
  through the afternoon Thursday.

Fog/low stratus bank over southern Lake Michigan has been
rapidly dissipating over the past couple hours, but has bled
inland into GYY. Cannot rule out some additional fog/stratus
redeveloping over the lake this evening, but with very light
flow in and above the boundary layer, it seems unlikely that low
CIGS or dense fog would penetrate inland to ORD/MDW this
evening.

Clear skies and light winds could allow for some shallow light
fog to develop toward sunrise, but confidence is low and only
added a TEMPO for MVFR VSBY at this time. Cannot rule out lower
VSBY or even LIFR CIGS at ORD and MDW overnight, but the
probabilities are low and opted to not include lower conditions
for ORD and MDW at this time. GYY is much trickier and forecast
confidence is much lower, for now opted for just a TEMPO for
LIFR CIGS for the first hour given the dissipating trends on
satellite, but certainly plausible that low CIGS could hang
around longer and/or dissipate then redevelop.

Any stratus or fog that does occur tonight should quickly
dissipate within an hour or so of sunrise as southerly winds
increase. Moderately gusty southerly winds are expected late
morning through the afternoon Thursday with peak gusts likely
tagging the mid-upper 20kt range at times. Gustiness will likely
abate after sunset Thursday evening.

- Izzi

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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